Liquid settling of fluorescent screens



Dec. 15, 1953 P. w. KRAUSE 2,662,829

LIQUID SETTLING OF FLUORESCENT SCREENS Filed Aug. 28, 1950 Fig. I.

Inverfltor: Paul W 'Krause,

Patented Dec. 15, 1953 UNITED' STATES PATENT OFFICE LIQUID SETTLING 0FFLUORESCENT SCREENS Paul W. Krause, Syracuse, N. Y., assignor to GeneralElectric Company, a corporation of New York Application August 28, 1950,Serial No. 181,799

7 Claims. (01. 117 3s.5) l 2 My invention relates to improved methods ofoff period of the excess liquid is much more rugliquid settlingfluorescent screens and particularly ged. These advantages combine torender the to the application of heat to the face of a cathscreens lessaffected by vibration on the settling ode ray tube during the settlingof the screen. conveyers and decrease the number of rejects due As thevolume of cathode ray tube manufacture 5 to defects in th screen.

has increased there has been a great demand for While the process isapplicable generally to the improvements in the processes of settlingthe settling of phosphors on an extended surfaceQit screens. Inaccordance with one general type of is particularly suited to cathoderay tubes. In the process that has found wide application thephosmanufacture of cathode ray tubes having envephors are settled to thetube face through a large 1 lopes of the typ including a metal cone as apart volume of liquid including a silicate solution and of the envelopeand a face plate of a thickness in an electrolyte, such as bariumnitrate or sodium the order of that commonly used for windows, thesulphate for example. A liquid settling process process is particularlyeffective since the required using barium nitrate and other alkalineearth amount of heat is readily transferred through the salts aselectrolytes is described and claimed in to face plate. These tubes arealso often made for copending Friedman application Serial No. use with awide sweep angle, that is, the slope 157,185, filed April 20, 1950 andassigned to the of the cone is large. In tubes of this character,assignee of this application. The application of the face plate area isvery large compared with screens to the cathode ray tube faces by thisgenthe area of the upper surface of the settling liquid era-1 tvne ofprocess involves both electrical and lo and the problem of getting aneven distribution chemical phenomena and, while many of thebasic of thphosphor particularly at the outer edges of considerations are known,the exact details of the the face plate is great. The present inventionis reactions involved are not thoroughly understood. particularlyadvantageous as applied to tubes of In accordance with prior art methodsall efforts this character.

to utilize a control of temperature to improve the My invention will bebetter understood by a screening process have been along the lines ofconsideration of examples of settling processes using refrigeratedliquid in the cathode ray tubes including the application of heat inaccordance and then controlling the ambient temperature to with theinvention. Applying my invention to the control the quality of thescreen. The control screening of 10-inch cathode ray tubes, for examthuseffected is very limited, involves a rather long :1, ple, the followingprocedure may be followed: The settling process, and is subject to greatdifficulty bulb is first supported in an upright position with ofcontrol on a factory floor due 'to unwanted the face down and 385 cc. of4% of barium nitrate changes in ambient temperature which are notsolution (water solution) is added to the bulb. readily eliminated. Forexample, it is often true Next, 2000 cc. of deionized water is added tothat the settling conveyors are located within a :35 the bulb to formwhat is called the cushion.

reasonably close distance to doors or other open- When the cushion waterhas become motionless ings in the factory buildings which are opened ata phosphor suspension made up of 2.4 grams of the various times with theresult that any process depowdered phosphor, 300 cc. of potassiumsilicate pending onaclose control of ambient temperature solution and300 cc. of water is poured on the is unsatisfactory. in cushion waterand the liquid allowed to settle.

In accordance with an important aspect of my Without the application ofany heat and at a Ve Ofl I h f u that the p p applicaroom temperature inthe order of 26 C. to 30 C. t of heat to the cat o r y tubes du ingsetapproximately one-half hour of settling is retling greatly Shortensthe Settling process and quired before the residual solution may bepoured i p v the q y of t resultant Screens- For 4.) off withoutdamaging the screen. In accordance example, the proper application ofheat, particuwith the present invention the face plate of the y t0 the eplates of the u dur ng the tube is subjected to radiant heating frominfra settling time hastens the jelling and binding red lamps or fromheating units which preferably action of the silicate solution, assistsin the proper operate at a red heat. If the water that is added and evendistribution of the p phor over the no to the bulb is at roomtemperature, it is preferable cathode ray tube face, renders the processindeto apply the heat a few minutes after the phospendent of variationsin ambient temperature, phor has been added. The heat is added for a andshortens the overall screening time. Also, the period, in the examplegiven, in the order of ten finished screen is of a finer texture and thescreen minutes during which time the screen is settled material in itswet or damp state during the poura. and obtains sufficient wet strengthto permit pouring of! of the supernatant liquid. The heat is appliedsubstantially uniformly over the cathode ray tube face and the resultanttemperature distribution within the tube, particularly with tubesemploying a metal cone type of envelope, is such as to aid indistributing the phosphor evenly to the edge of the face plate. That is,the temperature is higher at the outer edge, due to the ready transferof heat to the metal cone. In tubes of the glass envelope type, the faceplate heating does not raise the liquid at the outer edge of the tube toa temperature higher than the central position to the extent that itdoes with the metal cone type of envelope, and this desired temperaturedistribution may be obtained in either glass or metal types by addingadditional heat near the outer rim of the tube, as by surrounding itwith a heating unit, for example, or by starting with refrigeratedliquid as will be described in more detail at a later point in thspecification.

I'he exact amount of heat to be added is not critical but certain limitsmust be observed in order not to effect detrimentally the distributionof the phosphor or to deteriorate the brightness of the finishedphosphor screen. On a ten-inch tube, for example, to which the heat isapplied for a period of ten minutes, the pour-off temperature of theliquid was approximately 45 C. Pour-off temperatures as high as 80 havebeen employed. peratures of the above magnitude the actual face platetemperatures may reach as much as 150 C. to 160 C. While the processdescribed above may be employed with any phosphor which is notdetrimentally affected by the application of .l

the heat, it has been used extensively with a zinc sulphide, zinccadmium sulphide phosphor, which is one of the very widely usedphosphors in the manufacture of television receiving tubes.

The potassium silicate solution referred to in the above example of thescreening process is prepared by diluting a commercially availablesolution with an equal amount of water. The commercially availablesolution has, for example, the following specifications: lK O:3.9 SIO2,percentage -K2O='7.8%, and specific gravity=-l.25. .As is wellunderstood, sodium silicate and variations of the above potassiumsilicate solution may be employed.

Also in the above example the undiluted potassium silicate solution wasused in the amount of 150 cc. of a total liquid volume of about threeliters, or in other words, about a 5% solution. The concentration may bevaried appreciably, for example, between 2 /2 to 10 Instead of delayingthe application of heat until a few minutes after the introduction ofthe phosphor into the tube in the order of 3 or 4 minutes, verysuccessful application of the screen, including a good distribution, hasbeen obtained by starting with the original liquid introduced into thebulb at a temperature substantially below room temperature, in the orderof 16 C., for example, and applying the heat to the tube face forseveral minutes before the phosphor is introduced. This processinvolving the refrigeration of the liquid and preheating up desirablecurrents (by raising the liquid at the rim to a higher temperature thanthat at the central part of the tube) to assist in the distribution ofthe phosphor over the screen. The heat is applied for a total periodsomewhat in the order of ten minutes after the screen material isintroduced.

In carrying out the present invention, it is In raising the liquid topour-off tem- Molecular ratio necessary to accomplish the pour-off ofthe residual liquid reasonably promptly since the accelerated jelling ofthe silicate, as a result of the heat, renders pour-off diflicult if thej elling process is carried too far.

It will be apparent that variations may be made in heating time, finalpour-off temperature, and the like without departing from my inventionin its broader aspects. It must be borne in mind, however, that the heataffects the distribution of the phosphor, and this is a substantialbenefit if the heat is applied to aid in distributing the phosphor tothe edge of the face plate.

In the drawing I hav illustrated a settling conveyer suitable forcarrying out my invention on a continuous process basis. In the drawingFig. l is an elevational view of a part of the conveyer at the pour-offend thereof and Fig. 2 is a perspective View of a portion of theconveyer illustrating the position of the heating units employed forheating the face plates of the tubes While the screens are settled.Referring now to th drawing, the conveyer includes a plurality ofmovable supports or plates I, each of which is recessed appropriately toreceive the rim of a cathode ray tube envelope and support it ininverted position. The supports are provided with rollers 2 which rideon a suitable track provided by a rigid structural member such as thechannel 3. It will be appreciated that a similar channel is providedalong the opposite side of the conveyer and that as many supports I maybe provided in side-by-side relationship as are desired to give theconveyer the desired capacity. The supports l are mechanically linkedtogether by a suitable sprocket 5.

The cathode ray tube envelopes illustrated in Figs. 1 and 2 are of thetype including a metal cone 1, a glass neck 8 and a glass face plate 9.As previously indicated, the envelopes are supported in invertedposition in suitable recesses formed in the supports I and are retainedtherein by suitable pivoted clamping arms 10 provided with envelopeengaging resilient spools II. The clamping arms are operated by an arml2 through an overcenter linkage designated generally by the numeral l3.As shown in Fig. 2, suitable heating units extend longitudinally underthe conveyer in the direction of the conveyer travel for that portion ofthe conveyer length traversed bythe tube envelope during the period orperiods in which it is desired to add heat to the face plates. Theseheating units may, for example, be in the form of long straight sheathunits, including a central conductor l4 and an outer sheath [5. Theunits are preferably supported within suitable semi-cylindricalreflector units I S.

Inasmuch as it is preferable to supply heat to the face plates onlyduring a predetermined portion of the travel of the tube envelopes alongthe conveyer, it will be understood that the heating units areappropriately placed. As illustrated in Fig. 1 these units are notemployed just prior to the pour-off positions which, as illustrated inFig. l, are those positions of the envelope during which the supports Ifollow the contour of the sprocket 5. It will be readily appreciatedthat the materials are loaded into the inverted envelopes at a suitablestation along the conveyer and that the speed of movement and the lengthof the coveyer are coordinated to provide the required settling timebetween the addition of materials and the pour-off of the supernatantliquid.

Screens manufactured in accordance with the present invention have theadvantage of being sufficiently rugged to withstand vibration on theconveyer without damage. Also, lost motion in the conveyer which tendsto cause a back wash during pour-off of the residual liquid does notproduce any detrimental effect on screens settled in accordance with thepresent invention because of the superior wet strength of these screensas compared with those settled by prior art processes.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. The method of liquid settling a fluorescent screen on the face plateof a cathode ray tube which comprises supporting the tube with the faceplate thereof downward, introducing a substantial quantity of liquidinto the tube including a silicate sol and a powdered phosphorsuspension, said liquid having a temperature not higher than thetemperature of the room in which settling is carried out, subjecting theface plate of the tube to infra red heating during settling of thephosphor from the suspension to raise the temperature thereofsubstantially above the temperature of the room in which the settling iscarried out to assist in the distribution of the phosphor and acceleratethe binding thereof to the face plate, and removing the residual liquid.

2. The method of liquid settling a fluorescent screen on the face plateof a cathode ray tube which comprises supporting the tube with the faceplate thereof downward, introducing a substantial quantity of liquid ata temperature between 16 C. and 35 C. into the tube including a silicatesol and a powdered phosphor suspension, subiecting the face plate of thetube to heating during formation of the screen until the temperature ofthe liquid in the tube is at a temperature within the range of 35 to 80degrees 0., the higher final temperatures corresponding to the higherinitial temperatures, and removing the residual liquid.

3. The method of liquid settling a fluorescent screen on the face of acathode ray tube which comprises supporting the tube with the face platethereof downward, introducing a substantial quantity of liquid into thetube including a silicate sol and a powdered phosphor suspension, saidliquid having a temperature not higher than the temperature of the roomin which settling is carried out, subjecting the face plate of the tubeto heating after the addition of the phosphor suspension for a period ofapproximately ten minutes to raise the temperature of the liquid withinthe tube substantially above the temperature of the room in which thesettling is carried out, and removing the residual liquid before thesilicate solution has appreciably jelled.

4. The method of liquid settling a fluorescent screen on the face plate01 a cathode ray tube which comprises supporting the tube with the faceplate thereof downward, introducing a substantial quantity ofrefrigerated liquid including a silicate sol, the temperature of theliquid being substantially below the temperature of the room in whichthe settling is carried out, subjecting the face plate of the tube toheating for a period of several minutes, then adding a suspension ofpowdered phosphor, and continuing the heating for a substantial periodafter the addition of the phosphor and during the formation of thescreen to raise the temperature of the liquid in the tube substantiallyabove the starting temperature, and removing the residual solution.

5. The method of liquid settling a fluorescent screen on the face plateof a cathode ray tube which comprises supporting the tube with the faceplate thereof downward, introducing a substantial quantity of water at atemperature between 16 C. and 35 C. into the tube including a silicatesol and a powdered suspension of a zinc sulphide, zinc-cadmium sulphidephosphor, subjecting the face plate to heating during formation of thescreen for a period of approximately ten minutes to raise thetemperature of the liquid to a temperature between 35 and degrees C'.,the higher final temperatures corresponding to the higher startingtemperatures, and pouring off the residual solution.

6. The method of liquid settling a fluorescent screen on the face plateof a cathode ray tube which comprises supporting the tube with the faceplate thereof downward, introducing a substantial quantity of liquidinto the tube including a silicate sol and a powdered phosphorsuspension, said liquid having a temperature not higher than thetemperature of the room in which settling is carried out, applying heatto the tube during settling of the phosphor and formation of the screenincluding the face plate to raise the temperature thereof substantiallyabove the temperature of the room in which the settling is carried outand to raise the temperature of the liquid near the rim of the faceplate to a higher temperature than the liquid at the center and removingthe excess solution.

7. The method of liquid settling a fluorescent screen on the face plateof a cathode ray tube which comprises supporting the tube with the faceplate thereof downward, introducing a substantial quantity ofrefrigerated liquid including a silicate sol, the temperature of theliquid being substantially below the temperature of the room in whichthe settling is carried out, subjecting the face plate of the tube toheating for a period of several minutes to set up convection currents inthe solution, and then adding a suspension of powdered phosphor andcontinuing the heating for a substantial period after the addition ofthe phosphor to raise the temperature of the liquid in the tubesubstantially above the starting tem perature, and removing the excesssolution.

PAUL W. KRAUSE.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,223,830 Leverenz Dec. 3, 1940 2,412,654 Sadowsky Dec. 17,1946 2,451,590 Tidik et a1 Oct. 19, 1948

1. THE METHOD OF LIQUID SETTING A FLUORESCENT SCREEN ON THE FACE PLATEOF A CATHODE RAY TUBE WHICH COMPRISES SUPPORTING THE TUBE WITH THE FACEPLATE THEREOF DOWNWARD, INTRODUCING A SUBSTANTIAL QUANTITY OF LIQUIDINTO THE TUBE INCLUDING A SILICATE SOL AND A POWDERED PHOSPHORSUSPENSION, SAID LIQUID HAVING A TEMPERATURE NOTHIGHER THAN THETEMPERATURE OF THE ROOM IN WHICH SETTLING IS CARRIED OUT, SUBJECTING THEFACE PLATE OF THE TUBE TO INFRA RED HEATING DURING SETTLING OF THEPHOSPHOR FROM THE SUSPENSION TO RAISE THE TEMPERATURE THEREOFSUBSTANTIALLY ABOVE THE TEMPERATURE OF THE ROOM IN WHICH THE SETTLING ISCARRIED OUT TO ASSIST IN THE DISTRIBUTION OF THE PHOSPHOR AND ACCELERATETHE BINDING THEREOF TO THE FACE PLATE, AND REMOVING THE RESIDUAL LIQUID.